We tell our patients to take their warfarin (Coumadin) in the afternoon, but our hospital pharmacist says that this medication may be taken at any time of day as long as the patient is consistent. Are prothrombin times (PTs) and international normalized ratios (INRs) affected by variations in dosing intervals?
—Kevin M. Harvey, MD, Midlothian, Va.

Theoretically, PTs and INRs may be affected by variations in dosing intervals. However, subtle differences of a few hours would be unlikely to make much difference for a given individual who takes his or her Coumadin on a daily, consistent basis. The traditional afternoon dosing of Coumadin is, in fact, primarily used for convenience (time to adjust dose if the morning INR is not at target) and to promote consistency.
—Christopher Ruser, MD (110-14)

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